Color-stabilized electrochromic devices

ABSTRACT

An electrochromic medium for use in a normally operating electrochromic device comprising an anodic material and a cathodic material wherein both of the anodic and cathodic materials are electroactive and at least one of the anodic and cathodic materials is electrochromic, an additive, and means associated with the additive for maintaining a colorless or nearly colorless electrochromic medium while the electrochromic medium is in a high transmission state relative to an electrochromic medium without the additive

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application is a continuation of U.S. application Ser. No.09/377,455, filed Aug. 19, 1999

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates in general to electrochromicdevices, and more particularly, to normally operating, color-stabilizedelectrochromic devices having an electrochromic medium comprising one ormore additives, which serve to substantially preclude the formation ofundesirable residual color within the electrochromic medium while in itshigh transmission state.

[0004] 2. Background Art

[0005] Electrochromic devices have been known in the art for severalyears. While the utilization of electrochromic devices, such aselectrochromic mirrors, has become increasing popular among, forexample, the automotive industry, the development of undesirableresidual color within the electrochromic medium remains problematic.

[0006] Indeed, when a sufficient electrical potential difference isapplied across the electrodes of a conventional device, theelectrochromic medium becomes intentionally colored (i.e. a lowtransmission state) inasmuch as one or more of the anodic and thecathodic materials are oxidized and reduced, respectively. Specifically,the anodic materials are oxidized by donating electrons to the anode,and the cathodic materials are reduced by accepting electrons from thecathode.

[0007] For most commercially available devices, when the electricalpotential difference is removed or substantially diminished, the anodicand cathodic materials return to their native or unactivated state, andin turn, return the electrochromic medium to its colorless or nearlycolorless state (i.e. a high transmission state). The application andremoval of an electrical potential difference is conventionally known asa single cycle of the electrochromic device.

[0008] Scientists have observed that over a period of cycles and/ortime, during normal operation of the electrochromic device, theelectrochromic medium sometimes does not remain colorless in the hightransmission state. In some instances, even in the absence of anelectrical potential difference, either one or both of a portion of theanodic and cathodic materials are oxidized or reduced respectively,thereby forming residual oxidized and/or reduced materials. The residualoxidized anodic materials and/or the residual reduced cathodic materialsof the electrochromic medium can result in an undesired residualcoloration of the electrochromic medium.

[0009] Factors that are believed to facilitate the formation of theundesired residual oxidized anodic and/or reduced cathodic materialsinclude, among other things, impurities within the medium, thermaland/or photo chemical decomposition of one or more of the mediummaterials, and/or the permeation of water and/or oxygen into theelectrochromic medium.

[0010] It is therefore an object of the present invention to provide anelectrochromic medium with a color-stabilizing additive that remediesthe aforementioned detriments and/or complications associated withmaintaining a colorless or nearly colorless electrochromic device whilethe device is in its high transmission state.

SUMMARY OF THE INVENTION

[0011] The present invention is directed to an electrochromic medium foruse in a normally operating electrochromic device comprising: (a) ananodic material and a cathodic material, wherein both of the anodic andcathodic materials are electroactive and at least one of the anodic andcathodic materials is electrochromic, and (b) an additive, wherein theadditive is more easily reduced than the cathodic material

[0012] In a preferred embodiment of the invention, the additivesubstantially precludes the formation of a residual reduced cathodicmaterial while the electrochromic medium is in a high transmissionstate.

[0013] In another preferred embodiment of the invention, the additivecomprises either an oxidized form of the anodic material or anadditional material present in an oxidized form.

[0014] The present invention is also directed to an electrochromicmedium for use in a normally operating electrochromic device comprising(a) an anodic material and a cathodic material, wherein both of theanodic and cathodic materials are electroactive and at least one of theanodic and cathodic materials is electrochromic; and (b) an additive,wherein the additive comprises a reduced form of the cathodic material.

[0015] The present invention is further directed to an electrochromicmedium for use in a normally operating electrochromic device comprising:(a) an anodic material and a cathodic material, wherein both of theanodic and cathodic materials are electroactive and at least one of theanodic and cathodic materials is electrochromic; and (b) an additive,wherein the additive is more easily oxidized than the anodic material,and wherein the additive is selected from the group comprisingsubstituted ferrocenes, substituted ferrocenyl salts, and mixturesthereof.

[0016] The present invention is also directed to an electrochromicmedium for use in a normally operating electrochromic device comprising:(a) an anodic material and a cathodic material, wherein both of theanodic and cathodic materials are electroactive and at least one of theanodic and cathodic materials is electrochromic; and (b) an additive,wherein the additive comprises (1) a first component that is more easilyreduced than the cathodic material and (2) a second component that ismore easily oxidized than the anodic material

[0017] In a preferred embodiment of the invention, the first componentsubstantially precludes the formation of a residual reduced cathodicmaterial and the second component substantially precludes the formationof a residual oxidized anodic material while the electrochromic mediumis in a high transmission state.

[0018] In another preferred embodiment of the invention, the firstcomponent comprises either an oxidized form of the anodic material or anadditional electroactive material present in an oxidized form.

[0019] The present invention is additionally directed to anelectrochromic medium for use in a normally operating electrochromicdevice comprising (a) an anodic material and a cathodic material,wherein both of the anodic and cathodic materials are electroactive andat least one of the anodic and cathodic materials is electrochromic; (b)an additive; and (c) means associated with the additive for maintaininga colorless or nearly colorless electrochromic medium while such amedium is in a high transmission state relative to an electrochromicmedium without the additive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention will now be described with reference to thedrawings wherein:

[0021]FIG. 1 of the drawings is a cross-sectional schematicrepresentation of an electrochromic device fabricated in accordance withthe present invention;

[0022]FIG. 2 of the drawings is a two-dimensional plot showing thechange in a* value as a function of exposure time to an oxidativeenvironment for Experiments 1A-1B;

[0023]FIG. 3 of the drawings is a two-dimensional plot showing thechange in b* value as a function of exposure time to an oxidativeenvironment for Experiments 1A-1B;

[0024]FIG. 4 of the drawings is a two-dimensional plot showing thechange in a* value as a function of exposure time to an oxidativeenvironment for Experiments 2A-2D,

[0025]FIG. 5 of the drawings is a two-dimensional plot showing thechange in b* value as a function of exposure time to elevatedtemperatures for Experiments 2A-2D,

[0026]FIG. 6 of the drawings is a two-dimensional plot showing thechange in a* value as a function of exposure time to elevatedtemperatures for Experiments 3A-3B;

[0027]FIG. 7 of the drawings is a two-dimensional plot showing thechange in b* value as a function of exposure time to elevatedtemperatures for Experiments 3A-3B;

[0028]FIG. 8 of the drawings is a two-dimensional plot showing thechange in a* value as a function of exposure time to elevatedtemperatures for Experiments 4A-4B, and

[0029]FIG. 9 of the drawings is a two-dimensional plot showing thechange in b* value as a function of exposure time to elevatedtemperatures for Experiments 4A-4B.

DETAILED DESCRIPTION OF THE INVENTION

[0030] Referring now to the drawings and to FIG. 1 in particular, across-sectional schematic representation of electrochromic device 100 isshown, which generally comprises first substrate 112 having a frontsurface 112′ and a rear surface 112,″ second substrate 114 having afront surface 114′ and a rear surface 114,″ and chamber 116 forretaining electrochromic medium 124. It will be understood thatelectrochromic device 100 may comprise, for illustrative purposes only,a mirror, a window, a display device, a contrast enhancement filter, andthe like. It will be further understood that FIG. 1 is merely aschematic representation of electrochromic device 100. As such, some ofthe components have been distorted from their actual scale for pictorialclarity. Indeed, numerous other electrochromic device configurations arecontemplated for use, including those disclosed in U.S. Pat. No.5,818,625, which is hereby incorporated by reference in its entirety.

[0031] First substrate 112 may be fabricated from any one of a number ofmaterials that are transparent or substantially transparent in thevisible region of the electromagnetic spectrum, such as, for example,borosilicate glass, soda lime glass, float glass, natural and syntheticpolymeric resins or plastics including Topas®, which is commerciallyavailable from Ticona of Summit, N.J. First substrate 112 is preferablyfabricated from a sheet of glass having a thickness ranging fromapproximately 0.5 millimeters (mm) to approximately 12.7 mm. Of course,the thickness of the substrate will depend largely upon the particularapplication of the electrochromic device While particular substratematerials have been disclosed, for illustrative purposes only, it willbe understood that numerous other substrate materials are likewisecontemplated for use—so long as the materials are at least substantiallytransparent and exhibit appropriate physical properties, such asstrength to be able to operate effectively in conditions of intendeduse. Indeed, electrochromic devices in accordance with the presentinvention can be, during normal operation, exposed to extremetemperatures as well as exposed to substantial UV radiation, emanatingprimarily from the sun.

[0032] Second substrate 114 can be fabricated from similar materials asthat of first substrate 112. However, if the electrochromic device is amirror, then the requisite of substantial transparency is not necessary.As such, second substrate 114 may, alternatively, comprise polymers,metals, glass, and ceramics—to name a few. Second substrate 114 ispreferably fabricated from a sheet of glass having a thickness rangingfrom approximately 0.5 mm to approximately 12.7 mm. If first and secondsubstrates 112 and 114 , respectively, are fabricated from sheets ofglass, then the glass can optionally be tempered prior to or subsequentto being coated with layers of electrically conductive material (118 and120).

[0033] One or more layers of electrically conductive material 118 areassociated with rear surface 112″ of the first substrate. These layersserve as an electrode for the electrochromic device. Electricallyconductive material 118 is desirably a material that: (a) issubstantially transparent in the visible region of the electromagneticspectrum; (b) bonds reasonably well to first substrate 112; (c)maintains this bond when associated with a sealing member; (d) isgenerally resistant to corrosion from materials contained within theelectrochromic device or the atmosphere; and (e) exhibits minimaldiffusion or specular reflectance as well as sufficient electricalconductance. It is contemplated that electrically conductive material118 may be fabricated from fluorine doped tin oxide (FTO), for exampleTEC glass, which is commercially available from Libbey Owens-Ford-Co, ofToledo, Ohio, indium doped tin oxide (ITO), doped zinc oxide or othermaterials known in the art.

[0034] Electrically conductive material 120 is preferably associatedwith front surface 114′ of second substrate 114 , and is operativelybonded to electrically conductive material 118 by sealing member 122. Ascan be seen in FIG. 1, once bonded, the sealing member and thejuxtaposed portions of electrically conductive materials 118 and 120serve to define the inner peripheral geometry of chamber 116.

[0035] Electrically conductive material 120 may vary depending upon theintended use of the electrochromic device. For example, if theelectrochromic device is a mirror, then the material may comprise atransparent conductive coating similar to electronically conductivematerial 118 (in which case a reflector is associated with rear surface114″ of second substrate 114 ). Alternatively, electrically conductivematerial 120 may comprise a layer of reflective material in accordancewith the teachings of U.S. Pat. No. 5,818,625. In this case,electrically conductive material 120 is associated with front surface114′ of second substrate 114. Typical coatings for this type ofreflector include chromium, rhodium, silver, silver alloys, andcombinations thereof.

[0036] Sealing member 122 may comprise any material that is capable ofbeing adhesively bonded to the electronically conductive materials 118and 120 to, in turn, seal chamber 116 so that electrochromic medium 124does not inadvertently leak out of the chamber As is shown in dashedlines in FIG. 1, it is also contemplated that the sealing member extendall the way to rear surface 112″ and front surface 114′ of theirrespective substrates. In such an embodiment, the layers of electricallyconductive material 118 and 120 may be partially removed where thesealing member 122 is positioned. If electrically conductive materials118 and 120 are not associated with their respective substrates, thensealing member 122 preferably bonds well to glass. It will be understoodthat sealing member 122 can be fabricated from any one of a number ofmaterials including, for example, those disclosed in U.S. Pat. Nos.4,297,401, 4,418,102, 4,695,490, 5,596,023, 5,596,024, 4,297,401, andU.S patent application Ser. No. 09/158,423 entitled “Improved Seal ForElectrochromic Devices,” all of which are herein incorporated byreference.

[0037] For purposes of the present disclosure the electrochromic mediumis disclosed herein below as being a solution phase medium. However, itwill be understood that hybrid media and solid state media are likewisecontemplated for use. In a hybrid medium, one of the anodic or cathodicmaterials can be applied (in a solid form) to its respectiveelectrically conductive material. For example, a cathodic material, suchas tungsten oxide (WO₃) can be applied onto the surface of aconventional electrically conductive material. In a solid state mediumboth of the anodic and cathodic materials can be applied in a solid formto their respective substrates. In such an embodiment, the additive maystill be dissolved in the electrolyte positioned between the anodic andcathodic materials.

[0038] Electrochromic medium 124 is shown in FIG. 1, which generallycomprises an anodic material, a cathodic material, and acolor-stabilizing additive dissolved in at least one solvent. Duringnormal operation of device 100, the color-stabilizing additive enablesthe electrochromic medium 124 to remain colorless or nearly colorless inthe high transmission state Typically both of the anodic and cathodicmaterials are electroactive and at least one of them is electrochromic.Regardless of its ordinary meaning, the term “electroactive” will bedefined herein as a material that undergoes a modification in itsoxidation state upon exposure to a particular electrical potentialdifference Additionally, the term “electrochromic” will be definedherein, regardless of its ordinary meaning, as a material that has achange in its extinction coefficient at one or more wavelengths uponexposure to a particular electrical potential difference.

[0039] The cathodic material may include, for example, viologens, suchas methyl viologen tetrafluoroborate or octyl viologentetrafluoroborate. It will be understood that the preparation of theabove-identified viologens is well known in the art. While specificcathodic materials have been provided, for illustrative purposes only,numerous other conventional cathodic materials are likewise contemplatedfor use including, but by no means limited to, those disclosed in U.S.Pat. No. 4,902,108, which is hereby incorporated in its entirety byreference. Indeed, the only contemplated limitation relative to thecathodic material is that it should not adversely affect theelectrochromic performance of the device 100. Moreover, it iscontemplated that the cathodic material may comprise a solid transitionmetal oxide, including, but not limited to, tungsten oxide.

[0040] The anodic material may comprise any one of a number of materialsincluding ferrocene, substituted ferrocenes, substituted ferrocenylsalts, phenazine, substituted phenazines, phenothiazine, substitutedphenothiazines. Examples of anodic materials may includedi-tert-butyl-diethylferrocene,(6-(tetra-tert-butylferrocenyl)hexyl)triethylammonium tetrafluoroborate,(3-(tetra-tert-butylferrocenyl)propyl)triethylammoniumtetrafluoroborate, 5,10-dimethylphenazine, and3,7,10-trimethylphenothiazine It will be understood that numerous otheranodic materials are contemplated for use including those disclosed inthe previously referenced and incorporated '108 patent

[0041] For illustrative purposes only, the concentration of the anodicand cathodic materials can range from approximately 1 mM toapproximately 500 mM and more preferably from approximately 5 mM toapproximately 50 mM While particular concentrations of the anodic aswell as cathodic materials have been provided, it will be understoodthat the desired concentration may vary greatly depending upon thegeometric configuration of the chamber containing electrochromic medium124

[0042] For purposes of the present disclosure, the solvent of theelectrochromic medium may comprise any one of a number of materialsincluding sulfolane, glutaronitrile, dimethyl sulfoxide, dimethylformamide, acetonitrile, ethoxyethanol, tetraglyme and other similarpolyethers, nitriles, such as 3-hydroxypropionitrile,hydroacrylonitrile, 2-methylglutaronitrile, 2-acetylbutyrolactone,cyclopentanone, cyclic esters including gamma-butyrolactone, propylenecarbonate, ethylene carbonate and homogenous mixtures of the same. Whilespecific solvents have been disclosed as being associated with theelectrochromic medium, numerous other solvents are likewise contemplatedfor use.

[0043] In a first embodiment of the invention, the additive is moreeasily reduced than the cathodic material, and, during normal operationof the electrochromic device, serves to substantially preclude theformation of a residual reduced cathodic material while the device is inits high transmission state. The term “high transmission state” isdefined as the bleached state, the unpowered state, the unactivatedstate and/or the open circuit state of the electrochromic device, or astate where it is desirous for the electrochromic medium within thedevice to be colorless or nearly colorless. As previously discussed, aresidual reduced cathodic material can form from any one of a number ofdifferent reasons, and can leave the electrochromic medium undesirablytinted or colored, when it is desirous for the electrochromic medium tobe colorless or nearly colorless

[0044] In this first embodiment of the invention, the additive maycomprise an oxidized form of the anodic material, or alternatively, theadditive may comprise an additional material (other than the anodicmaterial) present in an oxidized form. Preferably, the additivecomprises a redox potential between that of both the anodic and cathodicmaterials. For example, the additive may comprise one or more materialssuch as ferrocinium salts, substituted ferrocinium salts, phenaziniumsalts, and substituted phenazinium salts. Specific materials mayinclude, for example, di-tert-butyl-diethylferrociniumtetrafluoroborate,(6-(tetra-tert-butylferrocinium)hexyl)triethylammoniumdi-tetrafluoroborate,(3-(tetra-tert-butylferrocinium)propyl)triethylammoniumdi-tetrafluoroborate, 5-methylphenazinium tetrafluoroborate. Preferablythe concentration of the additive ranges from approximately 0.01 mM toapproximately 10 mM.

[0045] In a second embodiment of the invention, the additive comprises areduced form of the cathodic material, and, during normal operation ofthe electrochromic device, serves to substantially preclude theformation of a residual oxidized anodic material while the device is inits high transmission state. Examples of suitable cathodic materials andtheir associated reduced species may include, for example, thoseidentified below: Cathodic Material Additive [Ru(NH₃)₆]³⁺ [Ru(NH₃)₆]²⁺[Fe(CN)₆]³⁻ [Fe(CN)₆]⁴⁻ [Cr(bpy*)₃]³⁺ [Cr(bpy*)₃]²⁺ [PMo₁₂O₄₀**]³⁻[PMo₁₂O₄₀**]⁴⁻

[0046] It will be understood that only the electrochemically relevantportion of the complexes have been disclosed and that theabove-identified complexes can be associated with any one of a number ofcations or anions to form a neutral species Preferably the concentrationof the additive ranges from approximately 0.01 mM to approximately 10 mM

[0047] In a third embodiment of the invention, the additive is moreeasily oxidized than the anodic material and is preferably selected fromone or more materials, such as substituted ferrocenes, substitutedferrocenyl salts, and mixtures thereof During normal operation of theelectrochromic device, the additives comprising the third embodimentserve to substantially preclude the formation of a residual oxidizedanodic material while the device is in its high transmission state.Specific examples of suitable materials includedi-tert-butyl-diethylferrocene,(6-(tetra-tert-butylferrocenyl)hexyl)triethylammonium tetrafluoroborate,and (3-(tetra-tert-butylferrocenyl)propyl)triethylammoniumtetrafluoroborate. While specific materials have been disclosed, forillustrative purposes only, numerous other materials that would be knownto those having ordinary skill in the art having the present disclosurebefore them are likewise contemplated for use. Preferably theconcentration of these additives ranges from approximately 0.01 mM toapproximately 10 mM

[0048] In a fourth embodiment of the invention, the additive comprises afirst component that is more easily reduced than the cathodic materialand a second component that is more easily oxidized than the anodicmaterial. During normal operation of the electrochromic device, thefirst component serves to substantially preclude the formation of aresidual reduced cathodic material and the second component serves tosubstantially preclude the formation of a residual oxidized anodicmaterial while the device is in its high transmission state.

[0049] The first additive component may comprise either an oxidized formof the anodic material, or an additional electroactive material presentin an oxidized form—or both with appropriate control of additivestoichiometry Examples of suitable first components include ferrociniumsalts, substituted ferrocinium salts, phenazinium salts, and substitutedphenazinium salts. Specific materials may include, for example,di-tert-butyl-diethylferrocinium tetrafluoroborate,(6-(tetra-tert-butylferrocinium)hexyl)triethyl ammoniumdi-tetrafluoroborate,(3-(tetra-tert-butylferrocinium)propyl)triethylammoniumdi-tetrafluoroborate, and 5-methylphenazinium tetrafluoroborate

[0050] The second additive component may comprise one or more materials,such as substituted phenazines, substituted ferrocenes, substitutedferrocenyl salts, and mixtures thereof. Specific materials may include,for example, 5-methylphenazinium,(6-(tetra-tert-butylferrocenyl)hexyl)triethylammonium tetrafluoroborate,(3-(tetra-tert-butylferrocenyl)propyl)triethylammoniumtetrafluoroborate, di-tert-butyl-diethylferrocene, and mixtures thereof.Preferably the concentration of both the first and second componentseach ranges from approximately 0.01 mM to approximately 10 mM.

[0051] It should be noted that the anodic and cathodic materials can becombined or linked by a bridging unit as described in InternationalApplication Ser. No. PCT/WO97/EP498 entitled “Electrochromic System.” Itis also possible to link the anodic and cathodic materials by otherconventional methods.

[0052] In addition, the electrochromic medium may also comprise othermaterials, such as light absorbers, light stabilizers, thermalstabilizers, antioxidants, viscosity modifiers including thickeners,and/or tint providing agents. Suitable UV-stabilizers may include: thematerial ethyl-2-cyano-3,3-diphenyl acrylate, sold by BASF ofParsippany, N.Y. under the trademark Uvinul N-35 and by Aceto Corp., ofFlushing, N.Y. under the trademark Viosorb 910; the material(2-ethylhexyl)-2-cyano-3,3-diphenyl acrylate, sold by BASF under thetrademark Uvinul N-539; the material2-(2′-hydroxy-4′-methylphenyl)benzotriazole, sold by Ciba-Geigy Corp.under the trademark Tinuvin P; the material2-hydroxy-4-methoxybezophenone sold by American Cyanamid under thetrademark Cyasorb UV 9; and the material 2-ethyl-2′-ethoxyalanilide soldby Sandoz Color & Chemicals under the trademark Sanduvor VSU—to name afew Thickeners include polymethylmethacrylate (PMMA) which iscommercially available from, among other chemical suppliers, AldrichChemical Co.

[0053] It will be understood that during normal operation, theelectrochromic devices of the present invention are intended to becycled between a high transmission state and a low transmission statenumerous times while maintaining a colorless or nearly colorlesselectrochromic medium during the high transmission state relative to anelectrochromic medium without the additive.

[0054] Electrochromic devices having as a component part acolor-stabilized electrochromic medium can be used in a wide variety ofapplications wherein the transmitted or reflected light can bemodulated. Such devices include rear-view mirrors for vehicles; windowsfor the exterior of a building, home or vehicle; skylights for buildingsincluding tubular light filters; windows in office or room partitions;display devices; contrast enhancement filters for displays; lightfilters for photographic devices and light sensors; and indicators forpower cells as well as primary and secondary electrochemical cells.

[0055] The electrochromic media of the present invention utilize manydifferent materials. The preparation and/or commercially availablesources are provided herein, unless the material is well known in theart. It will be understood that, unless specified otherwise, thestarting reagents are commercially available from Aldrich Chemical Co.,Milwaukee, Wis. and other common chemical suppliers. It will beunderstood that conventional chemical abbreviations will be used whenappropriate including the following: grams (g); milliliters (ml), moles(mol), millimoles (mmol), molar (M), and millimolar (mM)

Synthesis of (6-(tetra-tert-butylferrocenyl)hexyl)triethylammoniumtetrafluoroborate

[0056]

[0057] The synthesis of(6-(tetra-tert-butylferrocenyl)hexyl)trethylammonium tetrafluoroborateis a three step synthesis. First,6-bromo-1-(tetra-tert-butylferrocenyl)2-hexanone is prepared. Second,the ketonic product is converted to6-bromo-1-(tetra-tert-butylferrocenyl)hexane, which in turn, issubsequently converted into (6-(tetra-tertbutylferrocenyl)hexyl)triethylammonium tetrafluoroborate.

Preparation of 6-bromo-1-(tetra-tert-butylferrocenyl)-2-hexanone

[0058] First, a nitrogen purged flask was charged with 350 ml ofdichloroethane, 50.0 g (122 mmol) of tetra-tert-butylferrocene (preparedaccording to T. Leigh, J. Am. Chem. Soc. 1964, 3294-3302), and 19.3 ml(126 mmol) of 6-bromohexanoyl chloride. Second, the solution was cooledto 0 degrees centigrade, whereupon 13.3 g (100 mmol) of AlCl₃ wascharged into the reaction vessel in 3 equal portions at two hourintervals. It will be understood that the freshness and/or purity of theAlCl₃ can impact the degree of substitution of, for example, tert-butylgroups on a cyclopentadienyl ligand. Third, the reaction mixture wasthen slowly poured into 300 ml of agitating H₂O. Fourth, theorganic-aqueous mixture was charged with a sufficient quantity ofdiethyl ether so that an organic layer was appreciably formed on top ofthe aqueous layer Fifth, 50 ml of concentrated hydrochloric acid (HCl)was charged into the vessel. Sixth, approximately 2-5 g of zinc dust wascharged into the vessel to reduce any ferrocinium species present in theaqueous layer to the ether soluble ferrocene Once the layers wereclearly defined, they were separated and the aqueous layer was extractedwith 200 ml of diethyl ether (Et₂O). The two organic portions werecombined and washed with NaHCO₃ and brine. Next the organic solution wasdried over MgSO₄. The organic solution was then decanted from the MgSO₄and filtered. Next, the solvent was removed by rotary evaporation toyield a red oil The red oil was applied to a vacuum assisted silica gelcolumn and washed with hexane to remove any residual ferrocene Theproduct was eluted with Et₂O. Upon solvent removal and cooling in afreezer, 64.29 g of 6-bromo-1-(tetra-tert-butylferrocenyl)-2-hexanonewas isolated as a red solid.

Preparation of 6-bromo-1-(tetra-tert-butylferrocenyl)hexane

[0059] First, 2.27 g (17.02 mmol) of AlCl₃ was dissolved in 200 ml ofdry Et₂O in a Schlenk flask under controlled, positive nitrogenpressure. Second, the solution was cooled to 0 degrees centigrade and17.0 g (17.0 mmol) of 1.0M LiAlH₄ was charged into the flask viasyringe. The resulting suspension was warmed to room temperature andagitated for approximately 15 minutes. Next, 10.00 g (17.02 mmol) of theabove prepared 6-bromo-1-(tetra-tert-butylferrocenyl)-2-hexanone wasslowly added to the suspension. Once the addition of the ketonic productwas complete, the solution was heated to reflux for approximately 3hours, after which time the solution was cooled to room temperature. Thereaction was then quenched by slowly adding H₂O to the solution When nofurther exothermic reaction was observed, 250 ml of H₂O was added todilute the solution. The solution was then transferred to a separatoryfunnel, whereupon the organic layer was collected and the aqueous layerwas extracted with 100 ml of Et₂O The organic portions were combined andthen washed with NaHCO₃ and brine Next, the solution was dried overMgSO₄ The solution was then decanted from the drying agent and filtered.Next, the solvent was removed via rotary evaporation yielding ayellow-orange oil. The oil was dissolved in a small amount of hexane,applied to a vacuum assisted gel column, and eluted with more hexaneUpon solvent removal, 8.73 g of6-bromo-1-(tetra-tert-butylferrocenyl)hexane was isolated as ayellow-orange solid.

Preparation of (6-(tetra-tert-butylferrocenyl)hexyl)triethylammoniumtetrafluoroborate

[0060] First, 87.5 ml (628 mmol) of triethylamine (NEt₃), and 53.1 g (926 mmol) of 6-bromo-1-(tetra-tert-butylferrocenyl)hexane, and 50 ml ofacetonitrile were charged into a reaction vessel. The solution was thenheated to reflux for 4 days During this time the reaction wasperiodically monitored by thin layer chromatography (TLC), using hexaneas the eluent, for the disappearance of the starting material. Aftercooling to room temperature, the solvent was removed by rotaryevaporation and the product was precipitated by addition of Et₂O. Thebromide salt of the product was collected on a filter frit, and washedwith several portions of cold Et₂O. Next, the salt was dried in vacuo toyield an orange solid. An anion exchange was then performed bydissolving NaBF₄ in water and subsequently removing residual solidparticles via filtration. Next the bromide salt of the product wasdissolved in Methanol (MeOH) and the NaBF₄ dissolved in water was addedto the bromide salt solution. The methanol was slowly removed via rotaryevaporation until the product began to precipitate. The orangeprecipitate was collected on a filter frit, and the recrystallizationprocess was repeated. Finally the precipitate was dissolved in a minimumamount of MeOH, and Et₂O was added slowly to precipitate(6-(tetra-tert-butylferrocenyl)hexyl)triethylammonium tetrafluoroborate,an orange solid, which was collected on a frit, dried in vacuo, andstored for later use.

[0061] It will be understood that shorter and longer alkyl chainsubstituted groups, such as a propyl alkyl chain derivative can likewisebe synthesized using shorter or longer alkyl chain precursor reagents.

Synthesis of (6-(tetra-tert-butylferrocinium)hexyl)triethylammoniumdi-tetrafluoroborate

[0062]

[0063] First, 10.00 g (14.67 mmol) of the above-prepared(6-(tetra-tert-butylferrocenyl)-hexyl)triethylammonium tetrafluoroboratewas dissolved in 150 ml of dichloromethane (CH₂Cl₂). Next 5.0 g (25.7mmol) of AgBF₄ was added in 2 equal portions at a 5 minute interval.After agitating for 30 minutes, the solution was filtered and thesolvent was removed by rotary evaporation, yielding a green solid. Thegreen solid was redissolved in a minimal amount of CH₂Cl₂ and theproduct was precipitated by the addition of Et₂O. The solid was dried invacuo to yield 10.57 g of(6-(tetra-tert-butylferrocinium)hexyl)-triethylammoniumtetrafluoroborate as a dark green, crystalline solid.

[0064] First, a reaction flask was thoroughly purged with nitrogen andcharged with 300 ml of dichloroethane, 10.0 g (33.53 mmol) ofdi-tert-butylferrocene (prepared according to T. Leigh, J. Am. Chem.Soc. 1964, 3294-3302), and 7.44 ml (100.6 mmol) of freshly distilledacetyl bromide. The solution was agitated, cooled to 0 degreescentigrade, and charged with 8 94 g (67.06 mmol) of AlCl₃. The solutionwas held at 0 degrees centigrade for one hour and then warmed to roomtemperature. Agitation was maintained throughout the holding and warmingperiods. The reaction mixture was then transferred into a beakercontaining a mixture of agitating ice and dilute HCl. Next, Et₂O wasadded to form an organic layer on top of the aqueous layer. The organiclayer was separated—via separatory funnel and the aqueous layer wasextracted with 200 ml of Et₂O. The organic portions were combined andwashed with NaHCO₃ and brine and then dried over MgSO₄. Next, thesolution was decanted from the MgSO₄ and placed on a rotary evaporatorto remove the solvent, which yielded a red oil. The red oil was appliedto a silica gel column and washed with hexane to strip any residualstarting material from the product. The ketonic product was then elutedwith a mixture of ethyl acetate (EtOAc)/hexane (30:70 by vol.) Uponsolvent removal, 5.55 g of di-tert-butyl-diacetylfeirocene wascollected.

[0065] After the di-tert-butyl-diacetylfeirocene was prepared, a Schlenkflask under positive nitrogen pressure was charged with 25 ml of dryEt₂O. Second 0.35 g (2.61 mmol) of AlCl₃ was charged into the reactionflask Agitation was initiated and the AlCl₃ dissolved into solutionThird, 5.23 ml (5.23 mmol) of 1M L₁AlH₄ in Et₂O was charged into thereaction flask via syringe. The resulting suspension was agitated forapproximately 15 minutes. Fourth, 1.00 g (2.62 mmol) of theabove-prepared di-tert-butyl-diacetylferrocene was slowly charged intothe reaction vessel. Next, the solution was heated to reflux forapproximately 3 hours and then cooled to room temperature overnight withcontinuous agitation The reaction was then quenched by the slow additionof Et₂O to the solution. The organic layer was separated from theaqueous layer—via separatory funnel. Next, the aqueous layer wasextracted with 100 ml of wet Et₂O. The organic portions were combinedand washed with H₂O and brine, which was followed by drying over MgSO₄The solution was decanted from the drying agent and filtered. Next thesolvent was stripped via rotary evaporation, which yielded ayellow-orange oil. The oil was dissolved in a small amount of hexane,applied to a vacuum assisted silica gel column, and eluted with morehexane. Upon solvent removal, 0.627 g of di-tert-butyl-diethylferrocenewas collected and stored for later use.

[0066] First, 0.50 g (1.41 mmol) of the above-prepareddi-tert-butyl-diethylferrocene, 20 ml of CH₂Cl₂, and 0.282 g (1.45 mmol)of AgBF₄ were charged into a reaction vessel, whereupon agitation wasinitiated After approximately 2 hours of agitation, the solution wasfiltered and the solvent was removed by rotary evaporation, yielding agreen solid. The green solid was recrystallized by layered, solventdiffusion of Et₂O into a concentrated solution of crudedi-tert-butyl-diethylferrocinium BF₄ in CH₂Cl₂ The solid was dried undervacuum to yield 0 51 g of di-tert-butyl-diethylferrocinium BF₄ as a darkgreen, crystalline solid

[0067] In support of the present invention, several experiments wereconducted wherein electrochromic devices were prepared which comprised acolor-stabilizing additive, the color-stabilized performance of whichwere compared to analogous devices fabricated without acolor-stabilizing additive.

[0068] In discussing colors it is useful to refer to the CommissionInternationale de I'Eclairage's (CIE) 1976 CIELAB Chromaticity Diagram(commonly referred to the La*b* chart). The technology of color isrelatively complex, but a fairly comprehensive discussion is given by F.W. Billmeyer and M. Saltzman in Principles of Color Technology, 2^(nd)Ed., J. Wiley and Sons Inc. (1981), and the present disclosure, as itrelates to color technology and terminology generally follows thatdiscussion. On the La*b* chart, L defines lightness, a* denotes thered/green value and b* denotes the yellow/blue value. Each of theelectrochromic media has an absorption spectra at each particularvoltage that may be converted into a three number designation, theirLa*b* values. However, for the present discussion, the a* and b* valuesare most relevant inasmuch as: (1) a medium with an increased a* valueis more red; (2) a medium with a decreased a* value is more green; (3) amedium with an increased b* value is more yellow; and (4) a medium witha decreased b* value is more blue.

[0069] It will be understood that in each of the experiments providedbelow, the electrochromic materials were dissolved in propylenecarbonate (PC).

Experiment No. 1

[0070] In this experiment two electrochromic media were prepared bymixing the following materials together in the concentrations providedbelow. Experiment No. 1A Component Material Concentration CathodicOctylviologen BF₄ 34.0 mM Anodic 5,10-Dimethylphenazine 26.5 mM AdditiveNone — UV-Stabilizer T-butylpentylester of Tinuvin P* 50.0 mMUV-Stabilizer Tinuvin P 30.0 mM Thickener PMMA 3% by wt.

[0071] Experiment No. 1B Component Material Concentration CathodicOctylviologen BF₄ 34.0 mM Anodic 5,10-Dimethylphenazine 26.5 mM Additive(6-(tetra-tert-butylferrocenyl)-  5.0 mM hexyl)triethylammonium BF₄UV-Stabilizer T-butylpentylester of Tinuvin P 50.0 mM UV-StabilizerTinuvin P 30.0 mM Thickener PMMA 3% by wt

[0072] Each of the media were associated with an electrochromic mirrorfor testing Specifically, the mirror comprised two 2×5 inch substrates.The first substrate was coated with generally clear, conductive fluorinedoped tin oxide, and the second was coated with fluorine doped tin oxidewith a silver reflector on rear surface (114″). The substrates werespaced 137 microns apart for accommodating the medium.

[0073] As can be seen, Experiment No. 1A does not include an additiveand Experiment No. 1B comprises(6-(tetra-tert-butylferrocenyl)hexyl)triethylammonium BF₄ as anadditive. In order to simulate a harsh oxidative environment, each ofthe above-prepared media were placed into a conventional autoclave withan oxygen input line at 400 p.s i. at ambient temperature. The mediawere then evaluated for their color stability by obtaining La*b* valuesat predetermined intervals. The La*b* data for Experiment Nos. 1A and 1Bare provided below. Experiment No. 1—Autoclave Hours L a* b* ExperimentNo. 1A 0 88 93 −5 25  8 59 168 89 25 −5 44  8 64 336 89 07 −5 97  9 85504 88 94 −6 49 11 18 672 88 39 −7 44 14.11 840 87 72 −8 34 17 76 100887 41 −8.37 19 06 1176 87 1  −8 84 20 99 1344 86.9  −8 44 21 29 1512 8657 −8 44 22 2  1680 86 2  −8.44 23 58 1848 85 53 −8 97 25.68 2016 84 84−10.01  28 97 Experiment No. 1B 0 89 22 −4 78  9.35 168 89 52 −4 9  9 3336 89 31 −5 04  9 69 504 89   −5 27 10 44 672 88.81 −5 82 12 25 840 8848 −6 47 14.87 1008 88.41 −6 4  15 38 1176 88.26 −6 44 16 09 1344 87.96−6 34 16 4  1512 87.66 −6 4  16 92 1680 87.17 −6.81 18 49 1848 87 01 −679 19 11 2016 86.61 −6 67 19 47

[0074] Overall, the medium without the additive is turning substantiallymore green, which is shown in FIG. 2 as an increasing negative a* valueand in FIG. 3 as an increasing b* value Therefore, Experiment No. 1verifies that, indeed, the usage of the above-identified additiveprovides an effective mechanism to minimize the adverse colorationeffects associated with oxidative environments.

Experiment No. 2

[0075] In this experiment four electrochromic media were prepared bymixing the following materials together in the concentrations providedbelow: Component Material Concentration Experiment No. 2A CathodicOctylviologen BF₄ 34.0 mM Anodic 3,7,10-trimethylphenothiazine 26.5 mMAdditive None — UV-Stabilizer Tinuvin P 30.0 mM Thickener PMMA 3% by wt.Experiment No. 2B Cathodic Octylviologen BF₄ 34.0 mM Anodic3,7,10-trimethylphenothiazine 26.5 mM Additive(6-(tetra-tert-butylferrocenyl)-  2.0 mM hexyl)triethylammonium BF₄UV-Stabilizer Tinuvin P 30.0 mM Thickener PMMA 3% by wt

[0076] Component Material Concentration Experiment No. 2C CathodicOctylviologen BF₄ 34.0 mM Anodic 3,7,10-trimethylphenothiazine 26.5 mMAdditive (6-(tetra-tert-butylferrocinium)-  2.0 mMhexyl)triethylammonium (BF₄)₂ UV-Stabilizer Tinuvin P 30.0 mM ThickenerPMMA 3% by wt Experiment No. 2D Cathodic Octylviologen BF₄ 34.0 mMAnodic 3,7,10-trimethylphenothiazine 26.5 mM First Additive(6-(tetra-tert-butylferrocenyl)-  2.0 mM hexyl)triethylammonium BF₄Second Additive (6-(tetra-tert-butylferrocinium)-  2.0 mMhexyl)triethylammonium (BF₄)₂ UV-Stabilizer Tinuvin P 30.0 mM ThickenerPMMA 3% by wt

[0077] As can be seen, Experiment No. 2A does not include an additiveand Experiment Nos. 2B-2D comprise different ferrocene complexes asadditives. Each of the media (2A-2D) were associated with anelectrochromic mirror similar in construction to those described inExperiment No. 1 for color stabilization testing. Duplicate sets ofmirrors were constructed, half of which were placed in an autoclaveunder the same conditions identified in Experiment No. 1, while theother half were stored at 85 degrees centigrade to simulate exposure toprolonged elevated temperatures. The La*b* data was collected atpredetermined intervals, which is provided below. Hours L a* b*Experiment No. 2—Autoclave Experiment No. 2A 0 88.44 −3.45  7 76 16888.81 −3.46  7.67 336 88 67 −3.63  8.19 504 88.62 −3 49  8.28 672 87.86−3 75  9.82 840 86.76 −3.35 10.94 1008 86.45 −3.31 12 04 1176 86 33 −392 13.45 1344 86 01 −4.03 14.76 1512 85.71 −4 1  15 67 1680 84.64 −2.9915.62 1848 83 59 −1 68 15 15 2016 82 44  0 08 14 36 2184 81.42  0 75 1409 2352 80 99  2   13.55 Experiment No. 2B 0 88 8  −3.54 7 81 168 88.93−3.62 7.7  336 88 8  −3.73 7 78 504 88 9  −4   7 7  672 88 75 −4.25 7 83840 88.28 −4.21 8.2  1008 88.04 −4 53  8 89 1176 87 78 −4.96 10.07 134487.8  −5.59 12.3  1512 87 4  −5.82 13.93 1680 87 41 −6 12 14 96 1848 8721 −6.39 16 33 2016 87 13 −6 77 17 93 2184 86.95 −6 82 18 79 2352 86 58−6 42 18 89 Experiment No 2C 0 88 16 −4.35  8 16 168 88.5  −4 46  8 26336 88 15 −4 46  8 51 504 88.06 −4 5   8 86 672 87.46 −4 76  9 83 84086.98 −4 88 10 87 1008 86.71 −5 15 11 92 1176 86.51 −5 54 13.25 134485.61 −4.45 13 02 1512 84.66 −3.16 12 62 1680 82.3  −0 54 11 5  1848 8194  0 51 11 28 2016 80.37  2 3  10 63 2184 80.33  2 72 10 73 2352 79.46 3 91 10 46 Experiment No 2D 0 88 38 −3 96  8 15 168 88 51 −3 87  7 95336 88   −3 82  7 94 504 88 4  −3 9   7 93 672 87 67 −4 09  8 66 840 8715 −3 98  9 26 1008 87   −4 07 10 02 1176 86 47 −4.23 11.34 1344 86 17−4 35 12.6  1512 85 96 −4 53 13 63 1680 85 45 −4 77 14 32 1848 85 93 −521 15 21 2016 85 96 −5 6  16 31 2184 85 9  −5 74 17 25 2352 86 05 −5 8117 61 Experiment No. 2—Thermal Experiment No. 2A 0 88.3  −3.86  8.67 16787.34 −3 81  6 99 314 83.04 −5.69  1 29 478 79.62 −6.73 −2 58 651 77.62−7.54 −5 35 840 77.43 −7.3  −5 58 1025 75.06 −8.05 −8.39 1193 75.34−7.86 −7.75 1375 75.65 −8 24 −7 41 1543 74.97 −7 98 −8 44 1785 74.44−7.93 −8.74 1972 74.28 −8 06 −8.19 2261 74.94 −7.56 −8.03 Experiment No2B 0 88 55 −3 98  8 49 167 86 76 −4 41  6.15 314 82 74 −6.25  0 72 47881.28 −6.65 −1.07 651 80 37 −7.06 −2 23 840 81 15 −6.63 −1.07 1025 80.54−6.91 −1.35 1193 80.53 −6.78 −1 37 1375 80.03 −7.06 −1.98 1543 79.88−6.92 −2.29 1785 79 75 −6.98 −2.22 1972 78 95 −7 27 −3 07 2261 79 17 −703 −2.95 Experiment No. 2C 0 87.88 −5.14 9.26 167 88.04 −4 34 8 16 31488.06 −4.21 8 11 478 87.98 −4.11 8 02 651 87.94 −4.03 8 06 840 87.86 −394 7 94 1025 87.8  −3 88 8 19 1193 87.76 −3 92 8 19 1375 87.81 −3 9  829 1543 87.72 −3 83 8.12 1785 87.61 −3.87 8 15 1972 87.63 −3 82 8.232261 87 58 −3 74 8 06 Experiment No. 2D 0 88.26 −4.46 8 73 167 88 35−4.05 8.17 314 88 28 −3 91 8 09 478 88.2  −3.92 7 97 651 88 06 −3.96 78  840 87 68 −4 06 7.41 1025 87 26 −4.26 7.03 1193 87 07 −4 42 6 79 137586 49 −4 61 6 32 1543 86.54 −4 57 6 1  1785 86 28 −4 59 6.1  1972 86 16−4 87 5.72 2261 85 86 −4 56 5 75

[0078] In reference to the autoclave experiment, FIG. 4 depicts that themedia without the ferrocenyl additive (Autoclave Exp. 2A,2C) are turningmore red (the positive a* value) than the media with the ferrocenyladditive (Autoclave Exp 2B-2D) FIG. 5 graphically indicates the b*values for the media (Thermal Exp. 2A-2D) that were associated withmirrors stored at an elevated temperature. In particular, the mediacomprising a ferrocinium additive (Thermal Exp. 2C,2D) do notappreciably decrease in b* value. In comparison, the media without theferrocinium additive begin to “fail” or turn blue almost immediately

[0079] In addition, FIGS. 4 and 5 collectively demonstrate that a mediumcomprising both ferrocenyl as well as ferrocinium species maintainsrelatively constant a* and b* values in both oxidative and prolongedelevated temperature environments.

Experiment No. 3

[0080] In this experiment two electrochromic media were prepared bymixing the following materials together in the concentrations providedbelow: Component Material Concentration Experiment No. 3A CathodicMethylviologen BF₄ 34.0 mM Anodic (6-(tetra-tert-butylferrocenyl)- 21.8mM hexyl)triethylammonium BF₄ Additive None — UV-StabilizerT-butylpentylester of Tinuvin P 50.0 mM UV-Stabilizer Tinuvin P 30.0 mMThickener PMMA 3% by wt Experiment No. 3B Cathodic Methylviologen BF₄34.0 mM Anodic (6-(tetra-tert-butylferrocenyl)- 21.8 mMhexyl)triethylammonium BF₄ Additive (6-(tetra-tert-butylferrocinium)- 2.0 mM hexyl)triethylammonium (BF₄)₂ UV-Stabilizer T-butylpentylesterof Tinuvin P 50.0 mM UV-Stabilizer Tinuvin P 30.0 mM Thickener PMMA 3%by wt

[0081] As can be seen, Experiment No. 3A does not include an additiveand Experiment No. 3B comprises(6-(tetra-tert-butylferrocinium)hexyl)triethyl-ammonium BF₄ as anadditive. The media from Experiments 3A and 3B were placed intoelectrochromic windows configured similar to the mirrors as disclosed inExperiment No 2, except that a reflector was not associated with therear surface (114″) of the second substrate and the cell spacing was 250microns instead of 137 microns. The windows were stored at 85 degreescentigrade and La*b* data was collected at predetermined intervals,which is provided below. Experiment No. 3—Thermal Hours L a* b*Experiment No 3A 0 81.15 −4 01 19 45 267 81 18 −3 71 19 60 530 80 75−3.88 19 12 677 79.66 −4 39 17 55 841 78 68 −4.88 16 30 1014 77 44 −5.3614 04 1203 76.98 −5.77 13.58 1388 74 86 −6 45 10.64 1556 75.07 −6.6010.91 1738 73.85 −6.96  9.21 1906 73 65 −6.96  9.12 2148 73 13 −7.30 8.02 2335 71.31 −7.60  5 98 2624 71.30 −7.77  5.65 Experiment No 3B 080.28 −5 44 19 85 267 80 33 −5 15 20 07 530 80 24 −5 05 20 34 677 80 24−4 98 20 11 841 80 29 −5 02 20.20 1014 80 19 −4 78 20 35 1203 80.30 −503 20 16 1388 80.12 −4 74 20 48 1556 80.32 −4 89 20.27 1738 80.27 −4 7120.28 1906 80.20 −4 82 20.70 2148 80.20 −4 76 20.53 2335 79.82 −4.2820.68 2624 79.80 −4.64 20.77

[0082] shown in both FIGS. 6 and 7, the medium with the ferrociniumcomplex (Exp. 3B) is substantially more thermally stable than theanalogous medium without the additive (Exp. 3A). In fact, the mediumwithout the additive fails “blue” almost immediately (as indicated bythe decreasing b* values)

Experiment No. 4

[0083] In this experiment two electrochromic media were prepared bymixing the following materials together in the concentrations providedbelow. Experiment 4A is void of an additive. Component MaterialConcentration Experiment No 4A Cathodic Methylviologen BF₄ 16.0 mMAnodic Di-tert-butyl-diethylferrocene 16.0 mM Additive None —UV-Stabilizer Tinuvin 384 90.0 mM UV-Stabilizer Tinuvin P 30.0 mMThickener PMMA 3% by wt Experiment No 4B Cathodic Methylviologen BF₄16.0 mM Anodic Di-tert-butyl-diethylferrocene 16.0 mM AdditiveDi-tert-butyl-diethylferrocinium BF₄  2.0 mM UV-Stabilizer Tinuvin 38490.0 mM UV-Stabilizer Tinuvin P 30.0 mM Thickener PMMA 3% by wt

[0084] The above-prepared media were associated with electrochromicwindows constructed and tested analogous to those used in Experiment No3, and La*b* data was collected at predetermined intervals, which isprovided below. Experiment No. 4—Thermal Hours L a* b* Experiment No 4A0 81.81 −5.43   16.55  270 77.86 −7.61   10.32  487 77.43 −8.84   7 99753 75.61 −8.77   6.64 921 74.29 −8.76   5 49 1185 72.43 −9.49   2.841448 71.85 −9.73   2.08 1595 71.07 −9.92   1 17 1759 70.90 −9.95   0.971932 69.82 −10.45 −0 52 2121 70.74 −9.82   0 78 2306 69.51 −10.26 −0.772484 69.38 −10.31 −1 13 2666 68.65 −10.58 −2.11 2834 68.47 −10.51 −2.243076 68.34 −10 43 −2 36 3263 68.23 −10.61 −2 30 3552 67.66 −10.33 −3.003775 66.81 −10.70 −4 43 Experiment No. 4B 0 79.76 −6.60 17.34 270 79.59−6.13 17.37 487 81.44 −6.07 18.34 753 80.18 −5.78 17.35 921 79.50 −5.5517.23 1185 79.53 −5.53 17 36 1448 79.62 −5.48 17 49 1595 79.63 −5 43 1752 1759 79 60 −5.46 17 41 1932 79.75 −5.40 17 64 2121 79.49 −5 44 17 242306 79 51 −5 32 17.60 2484 79 56 −5.40 17.43 2666 79.75 −5.32 17 552834 79.55 −5.36 17 47 3076 79.33 −5 30 17.46 3263 79 54 −5 10 17.903552 79 22 −5 16 17 52 3775 79 46 −5.09 17 50

[0085]FIGS. 8 and 9 graphically demonstrate that, once again, the mediumwithout the additive (Exp. 4A) begins to fail rapidly relative to themedium comprising the additive

[0086] As can be seen from the above-provided experiments, theincorporation of one or more of the disclosed additives substantiallyimproves the color-stability of an electrochromic medium—even underoxidative environments or elevated temperatures

[0087] While the invention has been described in detail herein inaccordance with certain preferred embodiments thereof, manymodifications and changes therein may be effected by those skilled inthe art. Accordingly, it is our intent to be limited only by the scopeof the appending claims and not by way of details and instrumentalitiesdescribing the embodiments shown herein.

What is claimed is:
 1. An electrochromic medium for use in a normallyoperating electrochromic device, comprising: (a) an anodic material anda cathodic material, wherein both of the anodic and cathodic materialsare electroactive and at least one of the anodic and cathodic materialsis electrochromic; and (b) a color-stabilizing additive, wherein thecolor-stabilizing additive is more easily reduced than the cathodicmaterial.
 2. The electrochromic medium according to claim 1, wherein thecolor-stabilizing additive comprises an oxidized form of the anodicmaterial.
 3. The electrochromic medium according to claim 1, wherein thecolor-stabilizing additive comprises an additional material present inan oxidized form.
 4. The electrochromic medium according to claim 1,wherein the color-stabilizing additive is selected from the groupcomprising ferrocinium salts, substituted ferrocinium salts, phenaziniumsalts, substituted phenazinium salts, and mixtures thereof.
 5. Theelectrochromic medium according to claim 4, wherein thecolor-stabilizing additive is selected from the group comprisingdi-tert-butyl-diethylferrocinium tetrafluoroborate,(6-(tetra-tert-butylferrocinium)hexyl)triethylammoniumdi-tetrafluoroborate,(3-(tetra-tert-butylferrocinium)propyl)triethylammoniumdi-tetrafluoroborate, 5-methyl-phenazinium tetrafluoroborate, andmixtures thereof
 6. The electrochromic medium according to claim 1,wherein the concentration of the additive ranges from approximately 0 01mM to approximately 10 mM
 7. The electrochromic medium according toclaim 1, wherein the cathodic material comprises a viologen.
 8. Theelectrochromic medium according to claim 1, wherein the concentration ofthe cathodic material ranges from approximately 1 mM to approximately500 mM
 9. The electrochromic medium according to claim 1, wherein theconcentration of the cathodic material ranges from approximately 5 mM toapproximately 50 mM.
 10. The electrochromic medium according to claim 1,wherein the cathodic material comprises tungsten oxide.
 11. Theelectrochromic medium according to claim 1, wherein the anodic materialis selected from the group comprising ferrocene, substituted ferrocenes,substituted ferrocenyl salts, phenazine, substituted phenazines,phenothiazine, substituted phenothiazines, and mixtures thereof.
 12. Theelectrochromic medium according to claim 1, wherein the concentration ofthe anodic material ranges from approximately 1 mM to approximately 500mM.
 13. The electrochromic medium according to claim 1, wherein theconcentration of the anodic material ranges from approximately 5 mM toapproximately 50 mM.
 14. An electrochromic medium for use in a normallyoperating electrochromic device, comprising: (a) an anodic material anda cathodic material, wherein both of the anodic and cathodic materialsare electroactive and at least one of the anodic and cathodic materialsis electrochromic; and (b) a color-stabilizing additive, wherein thecolor-stabilizing additive is more easily oxidized than the anodicmaterial.
 15. The electrochromic medium according to claim 14, whereinthe color-stabilizing additive is selected from the group comprisingsubstituted ferrocenes, substituted ferrocenyl salts, and mixturesthereof.
 16. The electrochromic medium according to claim 15, whereinthe color-stabilizing additive is selected from the group comprising(6-(tetra-tert-butylferrocenyl)hexyl) triethylammoniumtetrafluoroborate,(3-(tetra-tert-butylferrocenyl)propyl)triethylammoniumtetrafluoroborate, di-tert-butyl-diethylferrocene and mixtures thereof.17. The electrochromic medium according to claim 14, wherein theconcentration of the additive ranges from approximately 0.01 mM toapproximately 10 mM.
 18. The electrochromic medium according to claim14, wherein the cathodic material comprises a viologen.
 19. Theelectrochromic medium according to claim 14, wherein the concentrationof the cathodic material ranges from approximately 1 mM to approximately500 mM
 20. The electrochromic medium according to claim 14, wherein theconcentration of the cathodic material ranges from approximately 5 mM toapproximately 50 mM
 21. The electrochromic medium according to claim 14,wherein the cathodic material comprises tungsten oxide.
 22. Theelectrochromic medium according to claim 14, wherein the anodic materialis selected from the group comprising ferrocene, substituted ferrocenes,substituted ferrocenyl salts, phenazine, substituted phenazines,phenothiazine, substituted phenothiazines, and mixtures thereof.
 23. Theelectrochromic medium according to claim 14, wherein the concentrationof the anodic material ranges from approximately 1 mM to approximately500 mM.
 24. The electrochromic medium according to claim 14, where theconcentration of the anodic material ranges from approximately 5 mM toapproximately 50 mM.
 25. An electrochromic device comprising at leastone substantially transparent substrate, and an electrochromic mediumaccording to claims 1 or 14 associated with the at least onesubstantially transparent substrate
 26. The electrochromic deviceaccording to claim 25, comprising a first substantially transparentsubstrate and a second substrate
 27. The electrochromic device accordingto claim 26, wherein the device is an electrochromic window.
 28. Theelectrochromic device according to claim 26, wherein the secondsubstrate is plated with a reflective material.
 29. The electrochromicdevice according to claim 28, wherein the reflective material isselected from the group comprising chromium, rhodium, silver, alloys ofthe same, and mixtures thereof.
 30. The electrochromic device accordingto claim 29, wherein the device is an electrochromic mirror.